1. Field of the Invention
This invention relates generally to methods and apparatus for identifying programs and the viewing habits of the public, and more particularly to a method and apparatus for identifying programs, such as television programs obtained from various sources, including video recorders.
2. Description of the Prior Art
Systems for identifying programs such as television programs that are broadcast or viewed are known. Such systems fall into various categories. These categories include manual systems wherein the viewer keeps a diary indicating all of the programs viewed; mechanical, electromechanical and electronic systems that sense the channel to which a television receiver is tuned; systems that detect identifying signals present in the television broadcast signal; and systems that monitor and analyze the program content of the broadcast signal utilizing image processing and correlation techniques to identify the program.
While all of these systems do provide a way to identify programs and to monitor the viewing habits of the public, the manual methods are slow in acquiring data and are prone to inaccuracies resulting from the entry of erroneous data that may be intentionally or unintentionally entered. Systems that monitor the channel to which a receiver is tuned overcome the drawbacks of the manual systems, but require access to the tuning mechanism of the receiver. Such access is becoming increasingly difficult with the advent of cable and pay television systems that utilize various converters and decoders, many of which are difficult to access. Moreover, such systems cannot identify programs played from a source such as a home video recorder. Systems that detect identification signals encoded on the broadcast signal overcome many of the accuracy and access disadvantages described above, but require the cooperation of the broadcasters who must encode the programs prior to broadcast for such systems to be effective. Consequently, such systems are useable only on a limited number of broadcasts, such as network broadcasts. Systems that monitor and analyze the content of the program itself theoretically eliminate the disadvantages of the other systems, but heretofore the information processing requirements of such systems rendered such systems impractical or uneconomical because of the computing capacity required to analyze the vast quantity of information present in a broadcast signals. Moreover, previous attempts to reduce the quantity of information processed tended to introduce inaccuracies.
An example of a system that utilizes the program content of a broadcast signal to identify the program is described in U.S. Pat. No. 3,919,479 to Moon et al. The Moon et al. system utilizes a non-linear analog transform to produce a low frequency envelope waveform, and the information in the low frequency envelope of a predetermined time interval is digitized to generate a signature. The signatures thus generated are compared with reference signatures to identify the program. However, the Moon et al. system generates the signatures continuously, and consequently, requires a large computer to process the data thus generated.
Another system that monitors the program content of a broadcast signal is disclosed in U.S. Pat. No. 4,230,990 to Lert Jr. et al. The system disclosed in the Lert Jr. et al patent reduces the amount of data that must be processed, as compared to the amount of data processed by the Moon et al. patent, by utilizing cues that are either externally generated or present in the program material to initiate the signature generation and correlation process only after a cue has been detected. However, the system disclosed in the Lert Jr. et al. patent is designed to monitor the programs broadcast by broadcasting stations such as network affiliated stations in order to determine whether they are broadcasting the programs required by the networks to be broadcast, rather than as a system for determining the viewing habits of the public. Thus, many of the problems that occur when the habits of a television viewer are being monitored, such as, for example, frequent channel changing, and the problems that occur in identifying programs that are recorded and subsequently played back by a home video recorder are not addressed.